Hi everyone. I have wide plank engineered oak floors glued down on a concrete substrate. The installation was completed about 2 years ago. In one area of a room, I have noticed that when I walk across it, there is a sensation that the floor is very slightly sloping down. The boards don't move at all or make noise, and when I knock on the area it sounds solid (i.e. not a hollow spot), but it almost feels like there's a slight decline once I reach a certain point and keep going (and on the flipside, it feels like a slight incline going the other direction). It's subtle but I notice it. Not sure if I am describing that clearly but is this a concern? Does it mean my subfloor wasn't properly leveled and this could be a future failure point? I'm surprised I could notice something like that. Thank you!

Edit: I've noticed this for the last 2 years, so it's not new / hasn't changed, but never really thought about it until recently and I'm worried about it becoming a future failure spot.

Probably won't be a problem if it's been two years. Most failures occur within the first year after installation. It's not broken, no need to fix.

Thank you Ken